This invention is directed to an improved attachment for a bench grinder to hold drill bits or other tools in preparation for sharpening. More specifically, it relates to attachments to temporarily convert a flat tool support into a tool support for sharpening drill bits, or for converting a tool rest for drill bits into a flat tool support.
Tools commonly used for cutting, such as chisels, gouges, planes, knives and lawn mower blades, have cutting surfaces that do not function properly if not kept sharp and free of surface imperfections. Dull blades require application of more force to the tool in order to cut a workpiece, potentially cutting too deeply or posing a safety hazard. Surface imperfections in such tools can impart defects in the cut surface of the workpiece, particularly during woodworking. A chisel or planer with a gouge in the cutting surface will leave an imperfection on a workpiece that requires additional sanding or finishing to obtain an acceptable surface appearance.
Drill bits also become dull with use, and it is advantageous to be able to use a grinder to restore the cutting edge to its original quality. For optimum sharpness, the tip of a drill bit cannot simply be held flat against a grinding surface. The tip of the drill bit forms a cone whose sides slope at an angle of 118xc2x0 from the sides of the drill bit. Maintenance of the optimum cutting surface requires that the conical shape be retained as much as possible. It is therefore necessary that the bit be held to the grinding surface at a 62xc2x0 angle as precisely as possible. In addition, the bit should be continuously rotated to minimize formation of flat areas on the cone.
Bench grinders are commonly used in the home to sharpen tools with cutting edges that have become nicked, dull or worn. The grinder sharpens or repairs the cutting edge of such tools by wearing away a small portion of the metal until a sharp, flawless edge is achieved. An accessory commonly used with bench grinders is a tool rest or tool support that supports the tool at an appropriate height so that it can more easily be sharpened. A commonly used tool rest consists of a flat surface that is either permanently or removeably attached to the grinder. Without any tool rest, it is extremely difficult, even for an experienced workman, to hold a drill bit at precisely 62xc2x0 while rotating it for the length of time needed to sharpen the bit.
Even where the tool support surface can be tilted to various angles, in most cases, adjustment of the surface angle must be accomplished entirely by hand, setting up to four elements to lock the tool rest at a selected angle and elevation. Setting the proper elements and holding the round bit in the same position for consistent results is very difficult under these conditions.
More recently, grinders have become available with a permanently attached tool rest specifically designed with a V-shaped channel to hold drill bits in an appropriate position for sharpening. The groove is generally oriented to hold the drill bit at an angle of approximately 62xc2x0, characteristic of the shape of the cutting tip of the bit. However, use of this type of tool rest is not advantageous for use when sharpening many other types of cutting surfaces. For example, a chisel may be placed on the tool rest with a portion of the blade on the flat area of the tool rest and a portion of the blade over the V-shaped channel. A downward force on the blade during sharpening could cause the blade to shift into the V-shaped channel changing its angular orientation, wearing away the edge at an inappropriate angle and causing damage to a portion of the blade.
Further, the groove that holds drill bits at a characteristic angle of 62xc2x0 is not useful for other small items that may require sharpening. Removal of a nick or gouge in the blade of a flat head screwdriver, for example, would not benefit from this type of tool support, since the angle does not hold the screwdriver in a position appropriate for grinding.
Since no single tool rest optimally sharpens all types of tools, there exists a need for attachments for permanently mounted tool rests to convert easily and inexpensively from one type to another.
It is, therefore, an object of this invention to provide an improved attachment that adapts a tool rest to hold either flat tools or drill bits in an optimum position for sharpening.
It is another object of this invention to provide an improved drill bit sharpening attachment that mounts on a bench grinder without removal of an existing flat tool rest.
It is still another object of this invention to provide an improved adapter for converting a tool rest to a flat surface, without removal of a grooved tool rest for sharpening drill bits.
It is yet another object of this invention to provide an improved drill bit sharpening attachment that is easily removed, providing convenient access to a permanently installed flat tool rest.
The above-listed objects are met or exceeded by the present tool rest attachment, which features a removable platform for converting a flat tool rest to one specially designed to sharpen drill bits, or vice versa.
More specifically, the present invention provides an attachment for sharpening of either a tool or a drill bit with a bench grinder. The attachment is designed to be used on a grinder having at least one grinding surface and a tool rest that is attached with a tool rest fastener. The tool rest has a tool rest surface and attachment surface at right angles to each other.
The attachment has a tool-receiving plate with a bottom surface and a top surface. The bottom surface is shaped and configured to matingly engage the tool rest surface. The top surface comprises one of a flat surface and a surface having an angled V-shaped groove that is shaped and configured to receive a drill bit and hold it at a fixed elevation and angle relative to the grinding surface. If the top surface is flat, it is designed to support a tool at a fixed height relative to the grinding surface.
A slotted flange is normally attached to the tool-receiving plate. It is sized and configured to engage the slot with the tool rest fastener. While the tool-receiving plate rests on the tool rest surface, it abuts the flange against the attachment surface when the tool rest fastener is tightened, to hold the attachment immobile during use.
During use, the attachment acts as an adapter to convert a flat tool rest to one useful for sharpening drill bits or adapts a grooved tool rest to one with a flat support surface. Single tool rests that attempt to provide the versatility to accomplish both of these tasks, generally require many manual settings to change the height and angle of the tool rest. The attachment of the present invention permits conversion from one type of tool rest to another, without removal of the permanently mounted tool rest.
This attachment is very simple to use. When the different surface is required, the user need only loosen the fastener, drop the attachment into place and tighten the fastener again. In seconds, a sturdy, secure surface is available for grinding of either drill bits or other tools.
Removal of the attachment, and return to the original tool rest surface is equally simple. The user need only loosen the fastener, remove the attachment, and retighten the fastener in its original position. There is no need to replace the permanently mounted tool rest. Further, this attachment is easy and inexpensive to manufacture.
This attachment provides an additional advantage when sharpening drill bits. The groove in the attachment is designed to hold the bit in the exact optimum position of 62xc2x0. Compared to manually setting angles and positions on the tool rest, this method is more accurate and consistent, leading to sharper bits. Less grinding, and therefore less metal removal, is required to obtain a good edge, resulting in longer lasting tools.